I just finished college about a month ago and have been on numerous interviews. Nothing has ever came of them. Im worried, I dont want to be "that guy" who only works part time.

Its not like Im not a hard worker, I go to the gym for 2 hrs 5 times a week so I have no problem getting off my butt. I have anxiety issues and confidence problems. But I know at the end of the day I can get the job done, or at least give it 100 percent.

What can I do to appear better in interviews? The questions always stump me (whats your biggest weakness, etc) No idea what to say

Basically you tell them what they want to hear without sounding like a suck up. Also it does help to sound confident. Granted I've only had 2 interviews and the first one I was 16 and they would have hired anyone. The second one though I had 2.5 years of experience and I knew I was good at my job. Again it was an hourly job at Staples that I got but I still went in with confidence and when I left the interview I knew I was going to get hired.

I found that bringing up as much real world experience as possible gets really good reactions. And you have to understand who it that's interviewing you. When the sales manager asked me the best job I ever did helping a customer I made sure I told him about a time when I helped someone pick out all of their Christmas gifts at my store when they only stopped in for one video game. That was a good true story. Then I mentioned, casually, that I also sold her a few protection plans with all the stuff that she bought (and honestly I don't even know if that true it was so long ago) and I knew that was exactly what he wanted to hear because his job was to sell those plans to people. The other manager got stories of me working extra hours and doing whatever was asked of me. "Yeah I worked an extra 5 hours on the busiest weekend of the year and spent it cleaning up out backroom." Just real things (or at least realistic lies) that you did at previous work places that you would be able to do at the job you're interviewing for.

If you don't have much experience in your field just try to relate the job to whatever you actually do have experience with.

"What is one of your biggest weaknesses?" Easily they'll ask you this. Respond with something that't tough for you pertaining to the job requirement, but that you bust your ass to compensate.
ie. going for a economic or marketing job "I had a really tough time with calculus in college. However, I sought out extra help from the staff and friends and ended up getting an A in the class due to hard work."

"Why pick you over the other [more qualified] applicants?" Again, staple question. Be honest, even if you don't have the work experience like someone else does. State examples where your lack of experience was easily overcome with your hard work.
ie. going for a pharmaceutical company, "I really enjoyed learning all that I have and that's what separates me from others. I enjoy knowing that I still can learn more about the job, I and intend to deliver an outstanding performance while improving, rather than simply relying on what I've learned."